Anaerobic infections are caused by bacteria that can live in the absence of normal oxygen levels. Often, these infections arise from a puncture wound or damage to an area such as the gums where anaerobic bacteria live in low numbers. The introduction of these bacteria into a warm, low-oxygen environment allows them to grow rapidly. Anaerobic bacteria often are responsible for the classic pus-filled abscess seen from pricking oneself on a thorn or loose nail.

Since these bacteria are often introduced deep under the skin or in areas that are difficult to clean and bandage, anaerobic infections are somewhat more serious than other infections and must be treated swiftly to avoid permanent scarring or damage. Schedule a visit with the veterinarian immediately if your dog has received a puncture wound, injured their gums, or has any sort of boil or abscess.

If left untreated, an anaerobic infection has all of the right ingredients to lead to shock and in serious cases, death.

Common bacterial species include Bacteroides, Enterococcus, Proteus, and Clostridium.

Owners who notice their dog has received a bite, puncture wound or trauma to the gums should contact an available veterinarian right away, and if possible note the animal or object that caused the injury. Fever, swelling of the wound site, and reduction in appetite are all possible signs of an anaerobic infection and are cause for a trip to the veterinarian at the earliest opportunity. If a small animal bit your dog, and it is possible for you to safely capture it, do so and bring it to the veterinarian's office. Rabies, while not an anaerobic infection, is a serious concern for animal bites.

A veterinarian will make a physical inspection of the wound site, noting the appearance or discharge of pus as well as redness and/or swelling on-site, and may take a sample of any discharge. Be prepared to give a history of any previous veterinary treatment, as some of the antibiotics commonly prescribed can cause adverse reactions. The veterinarian may culture the discharge to identify the microorganism responsible, or take a blood sample. Blood testing is often helpful in determining the severity of the infection by measuring the levels of white blood cells. Bacterial infections that reach the blood stream are life-threatening and will be detected by this test. Urine testing will also reveal the presence of elevated levels of white blood cells, and if the urinary tract is infected, culturing the bacteria is possible with a sample.

The treatment for anaerobic infections is antibiotics, possibly in conjunction with supportive care, such as IV fluids, nutrition or rest. Often, if the infection is severe enough to produce an abscess with the production of pus, surgical intervention will be needed to drain the wound and expose it to oxygen. Sometimes this is as simple as lancing the boil or abscess and cleaning it out with a sterile antiseptic solution. In cases of deeper infections, such as in the uterus or thoracic cavity, a full surgical debridement is needed, where the surgeon will scrape out the dead tissue and clean the area. This may require a general anesthetic, which will allow your dog to sleep painlessly through the surgery. However, general anesthetics can sometimes cause your dog to behave in a confused or abnormal manner for a few days post-surgery.

As always, it is essential that owners follow the instructions of the veterinarian regarding post-surgical care and administration of medication. Some medicines are inactivated by others, and so making sure to give the full course of antibiotics as directed (i.e. with food, without food, or at specific times of day) is very important to avoid a relapse of the infection. Surgical dressing should be left in place unless directed by a veterinarian to remove them, and a ‘cone’ or other protective device used to prevent the dog from chewing on the dressing. Do not bathe your dog unless directed otherwise after major surgery, as even the cleanest water can introduce new bacteria to an already-weakened immune system.